Modern aircraft provide airspeed information to pilots in several ways including, for example, visibly distinguishable regions representing safe and unsafe airspeeds on the airspeed readout portion of an aircraft display graphic. When the airspeed drops to an unsafe level, warnings and alerts are provided. The Federal Aviation Administration (FAA) publishes airworthiness standards for aircraft that require that aircraft safety systems warn pilots of low airspeed conditions when an aircraft begins operating below an identified minimum airspeed (referred to hereinafter as a “low airspeed”). The FAA requires that the low airspeed warning be clearly distinguishable and continue until the low airspeed condition is corrected (14 C.F.R. 25.207).
Pursuant to satisfying FAA safety regulations, traditional aircraft safety systems generally provide the flight crew with aural, visible, and tactile warnings when airspeed drops to a designated low airspeed. The designated low airspeed used to trigger a low airspeed warning is based on a predefined stall speed that is aircraft specific and reflects aircraft characteristics such as wing lift, aircraft weight, wing shape, airfoils, and the like. Minimum operating speeds such as takeoff safety speed, takeoff climb speed, and landing approach speed are also related to stall speed. In addition, a variable known as “stick shaker speed” is related to stall speed. That is, stick shaker speed is an airspeed slightly above stall speed, at which a tactile warning (specifically, causing the entire column to shake) is generated. Stick shaker speed is employed because the natural vibration caused by airflow around the wings at stall speed may not be strong enough itself to provide an effective warning that the aircraft is approaching stall speed.
Traditional aircraft warning systems utilize a scale factor to modify a combination of the stick shaker speed and an aircraft minimum operating speed to generate a low airspeed alert. The scale factor represents a safety margin, and the result of the modification is a low airspeed warning that occurs slightly ahead of the stick shaker speed, providing a pilot with time to respond to the low airspeed condition by increasing engine thrust. However, even when a pilot responds to a low airspeed condition in a timely manner, the low airspeed condition is not corrected until the jet engine reaches the pilot selected engine thrust value, which can be several additional seconds.
Traditional aircraft warning systems employ a constant predetermined scale factor, regardless of altitude data and/or engine thrust data. In a low altitude situation, the response time produced by the traditional aircraft warning systems is significant in terms of pilot cognitive workload and overall safety. Consequently, an increase in response time for low altitude situations is desirable. Thus a system or method for generating a low airspeed warning that provides additional response time in low altitude situations is desired.